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According to an article on IBM.com, "a race condition is a situation in which two or more threads or processes are reading or writing some shared data, and the final result depends on the timing of how the threads are scheduled. Race conditions can lead to unpredictable results and subtle program bugs." . Although the article concerns Java, I have in general been taught the same definition.
As far as I know, simple operation of reading from RAM is composed of setting the states of specific input lines (address, read etc.) and reading the states of output lines. This is an operation that obviously cannot be executed simultaneously by two devices and has to be serialized.
Now let's suppose we have a situation when a couple of threads access an object in memory. In theory, this access should be serialized in order to prevent race conditions. But e.g. the readers/writers algorithm assumes that an arbitrary number of readers can use the shared memory at the same time.
So, the question is: does one have to implement an exclusive lock for read when using multithreading (in WinAPI e.g.)? If not, why? Where is this control implemented - OS, hardware?
Best regards, Kuba
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an easy way to fix "check and act" race conditions is to synchronized keyword and enforce locking which will make this operation atomic and guarantees that block or method will only be executed by one thread and result of the operation will be visible to all threads once synchronized blocks completed or thread exited ...
Preventing Race Conditions Race conditions can be avoided by proper thread synchronization in critical sections. Thread synchronization can be achieved using a synchronized block of Java code. Thread synchronization can also be achieved using other synchronization constructs like locks or atomic variables like java.
A race condition is an undesirable situation that occurs when a device or system attempts to perform two or more operations at the same time, but because of the nature of the device or system, the operations must be done in the proper sequence to be done correctly.
A Race condition is a scenario that occurs in a multithreaded environment due to multiple threads sharing the same resource or executing the same piece of code. If not handled properly, this can lead to an undesirable situation, where the output state is dependent on the order of execution of the threads.
Reading memory at hardware level is done sequentially - you don't need to worry about concurrency at this level. Two threads issue read instructions and all the necessary stuff - setting addresses on the address bus and actual reads are implemented by the memory access hardware in such way that reads will always work right.
In fact the same is true for read/write scenarios except that when read and write requests are interleaved you will get different results depending on timing and this is why you need synchronization.
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